Data interface circuit for portable terminal equipment

ABSTRACT

A data interface circuit for portable radio terminal equipment having wire and radio data communication functions, thereby capable of being applied to a variety of communication systems. For a communication using a radio network, the signal type is changed from a differential-ended-signal (DES) type highly influenced by noise to a single-ended-signal (SES) type hardly influenced by noise by an operation of the radio interface unit, thereby enabling the redundancy to noise to be increased. Furthermore, it is possible to provide various audio services by the audio signal processing control unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to portable data terminal equipment havinga communication function, and more particularly to a data interfacecircuit capable of connecting portable data terminal equipment to apublic switched telephone network (PSTN) and an analog cellular network,thereby enabling data transmission and reception.

2. Description of the Prior Art

Modems are digital communication equipment (DCE) for transmitting andreceiving data between data terminal equipment by use of channels in theaudio band. Such data terminal equipment is usually a personal computer.

FIGS. 1A and 1B are views for explaining the conventional concept ofdata communications in a data terminal equipment wherein datatransmission and reception are achieved using PSTN's. Data terminalequipment such as personal or portable computers carry out datatransmission and reception with other personal or portable computers viaa modem serving as DCE and PSTN. Used as an interface technique betweenthe data terminal equipment and the DCE is V.24, which is a standardscheme of Comite Consoltatif International pour Telegraphie etTelephonie (CCITT) typically called "RS232C". A data access arrangement(DAA) is used as an interface between the DCE and the PSTN, as ingeneral telephones. As shown in FIG. 1B, the modem, which is the DCE,includes a modem control circuit 1 and an analog interface circuit 2.The DAA includes a hybrid circuit 3 and a line transformer 4 and servesto protect terminal equipment connected to the PSTN from a surgevoltage. In this case, the hybrid circuit 3 is an impedance matchingcircuit for separating a transmitting signal Tx and a receiving signalRx on a transmission line from each other. The line transformer 4 servesto optimize a signal TIP transmitted from the data terminal equipment tothe PSTN and a signal RING received from the PSTN to the data terminalequipment for an impedance matching.

Recently, utilization of data transmission and reception using radionetworks, such as cellular networks, has been abruptly increasing. Inthis case, transmitting-side and receiving-side cellular phones carryout data transmission and reception with each other by a trunkingoperation of a base station, as shown in FIG. 2A. Since radio channelsare used in this case, as different from the PSTN shown in FIG. 1,modems, which are DCE's, should be constructed to transmit and receiveradio frequency signals. Each modem should also be interfaced with theassociated cellular phone executing a cellular protocol. Generally, theinterface between the DCE and the cellular phone includes a hybridcircuit 3 and a line transformer 4. Additionally, this interface alsoincludes an Rx/Tx separating circuit 5. This Rx/Tx separating circuit 5serves to separate the transmitting signal Tx and the receiving signalRx on the transmission line from each other, similar to the hybridcircuit 3 used in the DAA. It is advantageous that the Rx/Tx separatingcircuit 5 is provided with an operational amplifier because input andoutput signals of cellular phones are generally single-ended signals. Asshown in FIG. 2B, signals on nodes A are used in this case, taking intoconsideration an impedance matching of the hybrid circuit 3.

In the above-mentioned conventional interface circuit, however, a signalattenuation occurs because the additional Rx/Tx separating circuitshould be used to connect the modem and the cellular phone.. As aresult, there is a limitation on data transfer rate. It is alsodifficult to provide various services because the interface circuit doesnot take into consideration the establishment of audio application pathat all.

SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a data interfacecircuit for portable data terminal equipment capable of making theportable data terminal equipment perform a communication function forwire or radio audio and data.

In accordance with the present invention, this object is accomplished byproviding a data interface circuit for connecting data terminalequipment to a public switched telephone network and an analog cellularnetwork, comprising: a soft modem adapted to control the overall system;an analog interface unit connected to the soft modem and adapted toconvert data received thereto or transmitted therefrom into aprocessible signal; a wire interface unit provided with a pair oftransmitting and receiving signal lines respectively connected to theanalog interface unit and the public switched telephone network; a radiointerface unit provided with a pair of transmitting and receiving signallines respectively connected to the analog interface unit and the analogcellular network via a cellular phone modulator; an audio signalprocessing control unit connected to the soft modem and adapted toperform compression and expansion of audio signals being transmittedtherefrom or received thereto as well as audio service functions; afirst switching unit adapted to switch a transmitting signal from theanalog interface unit between the wire interface unit and the radiointerface unit; and a second switching unit connected between the audiosignal processing control unit and the analog cellular network andadapted to switch signals transmitted from or received to the audiosignal processing control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and aspects of the invention will become apparent from thefollowing description of embodiments with reference to the accompanyingdrawings in which:

FIGS. 1A and 1B are block diagrams respectively explaining theconventional concept of data communications using a PSTN;

FIGS. 2A and 2B are block diagrams respectively explaining theconventional concept of data communications using an analog cellularnetwork; and

FIG. 3 is a block diagram illustrating a data interface circuit forportable data terminal equipment in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Where portable data terminal equipment is desired to have acommunication function, it should be constructed to transmit and receivedata as well as audio signals by utilizing both wire and radio channels.FIG. 3 illustrates a circuit capable of providing such a function. Thecircuit shown in FIG. 3 includes a soft modem 35 capable of programminga modem algorithm and constituted by a digital signal processor (DSP)and analog/digital (A/D) and digital/analog (D/A) converters to controlthe overall system. An analog interface unit 36 is connected to the softmodem 35. The analog interface unit 36 is adapted to convert datareceived thereto or transmitted therefrom into a processible signal(namely, analog or digital signal). The interface circuit furtherincludes an wire interface unit 44 provided with a pair of transmittingand receiving signal lines respectively connected to the analoginterface unit 36 and a PSTN, a radio interface unit 45 provided with apair of transmitting and receiving signal lines respectively connectedto the analog interface unit 36 and an analog cellular network via acellular modulator 40 of a cellular phone. To the soft modem 35, a audiosignal processing control unit 47 is connected which serves to performcompression and expansion of audio signals being transmitted therefromand received thereto as well as monitoring the signals. The interfacecircuit also includes a first switching unit 41 for switching atransmitting signal from the analog interface unit 36 and a secondswitching unit 43 for switching signals transmitted from or received tothe audio signal processing control unit 47.

The wire interface unit 44 includes a hybrid circuit 37 provided with areceiving signal line directly connected to the analog interface unit 36and a transmitting signal line indirectly connected to the analoginterface unit 36 via the first switching unit 41. The hybrid circuit 37serves to separate a transmitting signal Tx and a receiving signal Rxfrom each other. A line transformer 38 is connected to the hybridcircuit 37 via transmitting and receiving signal lines. The linetransformer 38 serves to optimize signals transmitted therefrom orreceived thereto. The wire interface unit 44 also includes a ringdetection/hook control unit 39 connected to the line transformer 38 viatransmitting and receiving signal lines and adapted to detect a ringsignal and control a hook signal.

The radio interface unit 45 includes a first amplifying stage 49 and asecond amplifying stage 52. The first amplifying stage includes a firstoperational amplifier 48 connected at a minus (-) terminal thereof tothe transmitting signal line of the interface circuit unit 36 via afirst resistor R1. The first operational amplifier 48 is also connectedat a plus (+) terminal thereof to the reference voltage terminal Vref ofthe first switching unit 41 via a second resistor R2. The plus terminalof the first operational amplifier 49 and the reference voltage terminalVref of the first switching unit 41 are connected in common to theground via a fourth resistor R4. An output signal from the firstoperational amplifier 48 is fed back to the minus terminal of the firstoperational amplifier 48 via a third resistor R3. On the other hand, thesecond amplifying stage 52 includes a second operational amplifier 50connected at a minus terminal thereof to the receiving signal line ofthe cellular phone modulator 40. The second operational amplifier 50receives at a plus (+) terminal thereof a reference voltage Vref. Anoutput signal from the second operational amplifier 50 is fed back tothe minus terminal of the second operational amplifier 50 via a fifthresistor R5. The second amplifying stage 52 further includes a thirdoperational amplifier 51 having a plus terminal to which the referencevoltage Vref is applied. The third operational amplifier 51 also has aminus terminal to which an output signal from the third operationalamplifier 51 is fed back.

The audio signal processing control unit 47 includes a parallel A/D andD/A converter 42 connected to the soft modem 35 via a data bus line, anda fourth operational amplifier 53 having a minus terminal connected to asignal line extending from a microphone 34 and a plus terminal connectedto the ground. An output signal from the fourth operational amplifier 53is fed back to the minus terminal of the fourth operational amplifier 53via a potentiometer 46. The output terminal of the fourth operationalamplifier 53 is also connected to the parallel A/D and D/A converter 42.The fourth operational amplifier 53 also includes a fifth operationalamplifier 54 having a minus terminal connected to a transmitting signalline of the parallel A/D and D/A converter 42 and a plus terminalconnected to the ground. An output signal from the fifth operationalamplifier 54 is fed back to the minus terminal of the fifth operationalamplifier 54 via another potentiometer 46. The output terminal of thefifth operational amplifier 54 is also connected to the speaker 33.

The first switching unit 41 includes four analog switches to send atransmitting signal from the analog interface unit 36 to the wireinterface unit 44 or the radio interface unit 45. That is, the firstswitching unit 41 includes a first switch a adapted to connect the plusoutput terminal of the analog interface unit 36 to the transmittingterminal Tx+ of the hybrid circuit 37 by its switching operation, asecond switch b adapted to connect the minus output terminal of theanalog interface unit 36 to the transmitting terminal Tx- of the hybridcircuit 37 by its switching operation, a third switch c adapted toconnect the plus output terminal of the analog interface unit 36 to theminus terminal of the first operational amplifier 48 of the wireinterface unit 45 by its switching operation, and a fourth switch dadapted to connect the plus terminal of the first operational amplifier48 of the radio interface unit 45 to the reference voltage terminal Vrefby its switching operation.

The second switching unit 43 includes a fifth switch e adapted toconnect the transmitting signal line of the radio interface unit 45 tothe receiving signal line of the parallel A/D and D/A converter 42 byits switching operation, a sixth switch f adapted to connect thereceiving signal line of the radio interface unit 45 to the transmittingsignal line of the parallel A/D and D/A converter 42 by its switchingoperation, a seventh switch g adapted to connect the transmitting,signal line of the radio interface unit 45 to the transmitting signalline of the parallel A/D and D/A converter 42 by its switchingoperation, and an eighth switch h adapted to connect the receivingsignal line of the radio interface unit 45 to the receiving signal lineof the parallel A/D and D/A converter 42 by its switching operation.

Operation of the data interface circuit according to the presentinvention will now be described.

The first and second switching units 41 and 43 use analog switches.Under control of the analog switches, the data interface circuitoperates in various modes. Where the cellular phone modulator 40 is tobe used for an audio telephone, the fifth and sixth switches e and f ofthe second switching unit 43 are switched on so that an audio signaloutput from the microphone 34 can be sent to the transmitting terminalTx of the cellular phone modulator 40 via the fourth operationalamplifier 53 and the fifth switch e. The audio signal is thentransmitted to the base station. After the audio signal is received bythe cellular phone modulator 40 via the base station, it is applied tothe speaker 33 via the fifth operational amplifier 54 by a switch-onoperation of the sixth switch f. If it is desired to compress and storethe content of communication, the eighth switch h of the secondswitching unit 43 is switched on. Under this condition, the content ofcommunication input at the microphone 34 or the receiving terminal Rx ofthe cellular phone modulator 40 can be compressed in the parallel A/Dand D/A converter 42 and then stored in the DSP of the soft modem 35.

For a data communication through a radio network, the third and fourthswitches c and d are switched on so that an output signal from theanalog interface unit 36 can be sent to the first amplifying stage 49 ofthe radio interface 45. The first amplifying stage 49 changes the signalfrom a differential-ended-signal (DES) type highly influenced by noiseto a single-ended-signal (SES) type hardly influenced by noise. Anoutput signal from the first amplifying stage 49 is sent to thetransmitting terminal of the cellular phone modulator 40. On the otherhand, a signal received by the receiving terminal Rx of the cellularphone modulator 40 is sent to the second amplifying stage 52 of theradio interface unit 45 which, in turn, changes the received signal fromthe SES signal type to the DES signal type. The changed signal isapplied to a terminal AUX of the analog interface unit 36.

For a data transmission through a wire network, the first and secondswitches a and b of the first switching unit 41 are switched on so thatan output signal from the analog interface unit 36 can be received tothe hybrid circuit 37 of the wire interface unit 44. The receivingsignal is separated by the hybrid circuit 37 and then optimized by theline transformer 38. Thereafter, the resulting signal is transmitted tothe PSTN under a control of the ring detection/hook control unit 39.Upon a data reception, a signal is received by the analog interface unit36 through a path reverse to that of the above-mentioned case. In thiscase, compression and storage of external audio signals received throughthe microphone 34 are carried out by the parallel A/D and D/A converter42 under a condition that all switches e to h of the second switchingunit 43 are switched off.

Compression and storage of other audio services, data or audio signalsare carried out in the audio signal processing control unit 47 under acontrol of the second switching unit 43. Where the content ofcommunication is to be checked during an execution of the modemfunction, the first switching unit 41 and the seventh switch g of thesecond switching unit 43 are controlled. For an automatic answeringmachine function of the radio network, the sixth to eighth switches f toh of the second switching unit 43 are switched on.

As apparent from the above description, the present invention provides adata interface circuit for portable radio terminal equipment having wireand radio data communication functions, thereby capable of being appliedto a variety of communication systems. For a communication using a radionetwork, the signal type is changed from DES to SES by an operation ofthe radio interface unit 45, thereby enabling the redundancy to noise tobe increased. Furthermore, it is possible to provide various audioservices by the audio signal processing control unit 47.

Although the preferred embodiments of the invention have been disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

What is claimed is:
 1. A data interface circuit for connecting dataterminal equipment to a public switched telephone network and a cellularnetwork, comprising:a soft modem adapted to control the overall system;an D/A/A/D interface unit connected to the soft modem and adapted toconvert data from analog to digital and digital to analog, respectively;a wire interface unit for connecting the D/A/A/D interface unit to thepublic switched telephone network; a radio interface unit for connectingthe D/A/A/D interface unit to the cellular network via a cellular phonemodulator; an audio signal processing control unit connected to the softmodem and adapted to perform acoustic transducing of audio signals andat least one of compression and expansion of said audio signals; a firstswitching unit adapted to switch a transmitting signal from the D/A/A/Dinterface unit to one of the wire interface unit and the radio interfaceunit; and a second switching unit adapted to selectively connect theaudio signal processing control unit to the cellular phone modulator soas to bypass said soft modem and yet provide said acoustic transducingin support of said cellular phone modulator, said second switching unitincludinga first switch adapted to selectively connect a transmittingsignal line of said radio interface unit to a receiving signal line ofsaid audio signal processing control unit; a second switch adapted toselectively connect a receiving signal line of said radio interface unitto a transmitting signal line of said audio signal processing controlunit; and a third switch adapted to selectively connect said receivingsignal line of said radio interface unit to said receiving signal lineof said audio signal processing control unit to provide a data componentof said compression.
 2. The data interface circuit in accordance withclaim 1, wherein the wire interface unit comprises:a hybrid circuitprovided with a receiving signal line directly connected to the D/A/A/Dinterface unit and a transmitting signal line indirectly connected tothe D/A/A/D interface unit via the first switching unit, the hybridcircuit being adapted to separate a transmitting signal and a receivingsignal from each other; a line transformer connected to the hybridcircuit and adapted to optimize the transmitting signal and thereceiving signal; and a ring detection/hook control unit connected tothe line transformer and adapted to detect a ring signal and control ahook signal so that data can be transmitted from and received to thepublic switched telephone network.
 3. The data interface circuit inaccordance with claim 1, wherein the radio interface unit comprises:afirst amplifying stage including a first operational amplifier having aminus input terminal connected by the first switching unit to atransmitting signal line of the D/A/A/D interface unit via a firstresistor, a plus input terminal connected to a reference voltageterminal by the first switching unit via a second resistor and an outputterminal fed back to the minus input terminal via a third resistor, theplus terminal and the reference voltage terminal of the first switchingunit being connected in common to the ground via a fourth resistor; anda second amplifying stage including a second operational amplifier and athird operational amplifier, the second operational amplifier having aminus input terminal connected to a receiving signal line of thecellular phone modulator, a plus input terminal receiving a referencevoltage and an output terminal fed back to the minus input terminal ofthe second operational amplifier via a fifth resistor, the thirdoperational amplifier having a plus input terminal receiving thereference voltage and a minus input terminal to which an output signalfrom the third operational amplifier is fed back.
 4. The data interfacecircuit in accordance with claim 1, wherein the audio signal processingcontrol unit comprises:a parallel A/D and D/A converter connected to thesoft modem via a data bus line; a first operational amplifier having aminus input terminal connected to a signal line extending from amicrophone, a plus input terminal connected to the ground and an outputterminal fed back to the minus input terminal via a potentiometer andconnected to the parallel A/D and D/A converter; and a secondoperational amplifier having a minus input terminal connected to atransmitting signal line of the parallel A/D and D/A converter, a plusinput terminal connected to the ground and an output terminal fed backto the minus input terminal of the said operational amplifier viaanother potentiometer and an output of which is connected to a speaker.5. The data interface circuit in accordance with claim 1, wherein thefirst switching unit comprises a plurality of analog switches forsending the transmitting signal from the D/A/A/D interface unit to thewire interface unit or the radio interface unit in a controlled manner.6. The data interface circuit in accordance with claim 1, wherein thesecond switching unit comprises:a fourth switch adapted to selectivelyconnect the transmitting signal line of the radio interface unit to thetransmitting signal line of the audio signal processing control unit. 7.The data interface circuit in accordance with claim 1, wherein saidsecond switching unit is also adapted to selectively connect said softmodem to said radio interface unit by way of said audio signalprocessing control unit, said audio signal processing control unit beingoperable to compress said audio signals exchanged with said radiointerface and being operable to provide such compressed audio signals tosaid soft modem.
 8. The data interface circuit in accordance with claim1, wherein said cellular network is an analog cellular network.
 9. Thedata interface circuit in accordance with claim 1, wherein said radiointerface unit is operable to exchange differential-ended (DE) signalswith said D/A/A/D interface and is also operable to convert said DEsignals to single-ended (SE) signals and to exchange said SE signalswith said cellular phone modulator.